Polypodal chelants for metallopharmaceuticals

ABSTRACT

Tripodal polyaminophosphonate chelants are disclosed, as well as chelates of the chelants with metal ions to form radiopharmaceutical and radioactive, MRI and X-ray or CT imaging compounds and compositions. Therapeutic and imaging methods of use are also disclosed.

FIELD OF THE INVENTION

This invention relates to a novel class of tripodalpolyaminophosphonates and metal chelates thereof, methods of preparingthe tripodal polyaminophosphonate chelants and metal complexes, andpharmaceutical compositions comprising the tripodal polyaminophosphonatechelants and metal chelates. This invention relates particularly to theuse of the new metal chelates as contrast agents for x-ray or MRIimaging. This invention also relates to the use of metal chelates usefulas diagnostic radiopharmaceuticals for imaging the skeleton, myocardialinfarction, infarctions of the spleen and bowel, inflammatory boweldisease, radiation injury, metastastic calcification, bone cancer, andvarious bone disorders. This invention also relates to the use ofradiometal chelates particularly useful as therapeuticradiopharmaceuticals for bone pain relief, bone marrow suppression, thetreatment of bone cancer, and various bone disorders.

BACKGROUND OF THE INVENTION

The development of a bone metastasis is a common and often catastrophicevent for a cancer patient. The number of patients with metastasticdisease is large among those who have breast cancer, prostate cancer,and lung carcinoma, as well as other tumors (Bouchet, L. G., et al. J.Nucl. Med. 2000, 41, 682-687). The pain, pathological fractures,frequent neurological deficits and forced immobility caused by thesemetastastic lesions significantly decreases the quality of life forcancer patient. The initial goal for the treatment is to relieve thepain, reduce narcotic medication requirement, and increase ambulation.

The use of radionuclides for the treatment of metastastic cancer startedin the early 1950's. It has been proposed that a radionuclide,particularly □-emitters, could be concentrated in the fast growingportion of the bone with minimal amounts of radiation reaching the softtissue or normal bone. Over the years, treatment of bone pain usingbone-seeking radiopharmaceuticals has been explored extensively. The useof radiopharmaceuticals which cause partial or total suppression oreradication of the bone marrow has become an accepted part of proceduresused to treat a patients with cancer such as leukemias, lymphomas,myelomas and Hodgkin's disease as well as in the treatment of patientssuffering from genetic disorders such as sickle cell anemia andthalassemia. Details on the use of therapeutic radiopharmaceuticals forbone pain palliation and treatment of bone metastases can be found inthe following references: Stanley, I. K. et al. Anticancer Res. 1988, 8,681-684; Serafini, A. N. J. Radiation Oncol. Biol. Phys. 1994, 30,1187-1194; McEwan, A. J. B. Semin. Nucl. Med. 1997, 27, 165-182;Krishnamurthy, G. T. and Krishnamurthy, S. J. Nucl. Med. 2000, 41,688-691; Bouchet, L. G., et al. J. Nucl. Med. 2000, 41, 682-687.

³²P-labeled orthophosphate (Silberstein, E. B. Semin. Oncol. 1993, 20,10-20) and ⁸⁹SrCl₃ (Ackey, D. and Yardly, J. Semin. Oncol. 1993, 20(suppl.), 27-31) are the first radiopharmaceuticals to be evaluated forthis purpose. U.S. Pat. No. 4,399,817 discloses the use of phosphoruscompounds containing a boron residue. The compounds were injected intothe body and accumulated in the skeletal system. The patient was thenirradiated with neutrons in order to activate the boron, and to give aradiation dose.

The drawback associated with ³²P and ⁸⁹Sr as palliative agents is thatboth isotopes are high-energy □-emitters with very long penetrationrange, which can result in significant irradiation of the marrowcompartment and depression of normal bone function. Therefore, it isimpossible to give therapeutic doses to the tumor without substantialdamage to normal bone and soft tissues.

Polyaminophosphonate chelants show very high affinity for hard cationssuch as Ca²⁺ and lanthanide metal ions. Metal chelates ofpolyaminophosphonates often localize in bone in a short period of time,probably in part due to interactions of the uncoordinated oxygen donorsin the polyaminophosphonate chelate with Ca²⁺ on the bone surface. Dueto their high bone uptake, radiometal chelates of polyaminophosphonatechelants have been studied as therapeutic radiopharmaceuticals forbone-pain palliation and for the treatment of bone cancer metastasis.European patent application No. 291,605 and U.S. Pat. No. 4,898,724disclose the use of Sm-153, Gd-159, or Ho-166 chelates for bone marrowsuppression. The lanthanide chelate contains a linearpolyaminophosphonate chelant selected fromethylenediaminetetramethylenephosphonic acid (EDTMP),diethylenetriaminepentamethylenephosphonic acid (DTPMP),hydroxyethylethylenediaminetrimethylenephosphonic acid (HEEDTMP),nitrilotrimethylenephosphonic acid (NTMP), ortris(2-aminoethyl)aminehexamethylenephosphonic acid (TTHMP). U.S. Pat.No. 4,882,142 discloses the use of Sm-153, Gd-159, or Ho-166 chelateswith 1,4,7,10-tetraazacyclododecane-tetramethylenephosphonic acid(DOTMP) for bone marrow suppression and other bone-related diseases. Thechelate ¹⁵³Sm-EDTMP (Quadramet®) has recently been approved by FDA forbone pain palliation. The chelate ¹⁶⁶Ho-DOTMP is under clinicalinvestigation for both bone pain palliation and the treatment of bonemetastases. Despite their success, there is still a need for a bettertherapeutic radiopharmaceutical labeled with an appropriate lanthanideradionuclide.

Prior to therapy it is necessary to obtain reliable diagnosticinformation and to this end several approaches have been tried. It isknown that phosphates and phosphonates have an affinity forhydroxyapatite crystals, and tend to localize in vivo in the regions ofbone metabolism, and in certain tumors, such as neuroblastoma. Theuptake of radiopharmaceuticals containing phosphonate chelant in tumorsis attributed to calcification in tumors. For example, U.S. Pat. No.3,974,268 discloses the use of technetium-99m (^(99m)Tc) chelates ofdiphosphonate chelants as skeletal imaging agents. The diphosphonate isused as both the bone targeting-agent and the chelating agent for^(99m)Tc. The properties of these radiopharmaceuticals, which lead totheir localization in bone, also allow for them to localize in softtissues bearing recognition features in common with bone. Localizationof such agents in areas of myocardial infarction is an example of oneapplication, which has proven diagnostically useful.Radiopharmaceuticals, which localize in bone, also have been shown tolocalize infarctions of the spleen and bowel, inflammatory boweldisease, radiation injury, as well as metastastic calcification.

Radionuclides, including but not limited to ^(99m)Tc, ^(117m)Sn, ¹¹¹In,⁶⁷Ga, ⁶⁸Ga, ⁸⁹Zr, ⁶²Cu, ⁶⁴Cu and ⁶⁷Cu, have been proposed for diagnosticimaging. The choice of the radionuclide depends largely on the physicaland nuclear properties (half-life and □-energy), availability, and cost.In general, generator-produced radionuclides are considered ideal, sincethe generator system consists of a long-lived parent isotope that decaysto a short-lived daughter isotope. The daughter can be easily separatedfrom the parent by either ion-exchange chromatography or solventextraction.

Nearly 80% of radiopharmaceuticals used in nuclear medicine are^(99m)Tc-labeled compounds. The reason for such a preeminent position of^(99m)Tc in clinical use is its extremely favorable physical and nuclearcharacteristics. The 6 h half-life is long enough to carry outradiopharmaceutical synthesis and to collect useful images. At the sametime, it is short enough to permit the administration of millicurieamounts of ^(99m)Tc radioactivity without significant radiation dose tothe patient. The monochromatic 140 KeV photons are readily collimated togive images of superior spatial resolution. Furthermore, ^(99m)Tc isreadily available from commercial ⁹⁹Mo-^(99m)Tc generators at low cost.

Various ^(99m)Tc-labeling techniques have been described in severalreviews (Liu, S. and Edwards, D. S. Chem. Rev. 1999, 99, 2235-2268;Jurisson, S. and Lydon, J. D. Chem. Rev. 1999, 99, 2205-2218; Anderson,C. J. and Welch, M. J. Chem. Rev. 1999, 99, 2219-2234; Volkert, W. A.and Hoffman, T. J. Chem. Rev. 1999, 99, 2269-2292; Liu, S., et al.Bioconjugate Chem. 1997, 8, 621-636). After radiolabeling, the resultingreaction mixture may optionally be purified using one or morechromatographic methods, such as Sep-Pack or high performance liquidchromatography (HPLC). The preferred radiolabeling procedures are those,in which the chelation can be achieved without post-labelingpurification.

Nuclear magnetic resonance (NMR) is based on the absorption ofradio-frequency energy by the magnetic moment of atomic nuclei insamples placed in a strong magnetic field. Conventional magneticresonance imaging (MRI) of human body relies mainly on the detection ofmost abundant type of nuclei, the hydrogen in water (and to some extent,fat). For discrimination of healthy and diseased tissues, adequatecontrast is essential. Such contrast depends not only on differences inwater concentration, but also on the NMR relaxation times T₁ and T₂,which in turn are related to local mobility and interactions. The MRIcontrast agent is used to improve diagnosis of disease by changingtissue signal intensity. Contrast agents increase both 1/T₁ and 1/T₂ tovarying degrees depending on their nature as well as the appliedmagnetic field. Agents such as gadolinium(III) that increase 1/T₁ and1/T₂by roughly similar amounts are best visualized using T₁-weightedimages since the percentage change in 1/T₁ in tissue is much greaterthan that in 1/T₁ (Caravan, P. et al. Chem. Rev. 1999, 99, 2293-2352).Iron-oxide particles generally lead to a much larger increase in 1/T₂than in 1/T₁ and are best seen with in T₂-weighted scans.

MRI diagnosis has become a widely accepted diagnostic modality for avariety of diseases. The availability of MRI devices has led to the useof MRI in medical examination for the detection and diagnosis of diseasestates and other internal abnormality. The continued use and rapiddevelopment of MRI has stimulated interest in the development of new MRIcontrast agents. Most of MRI contrast agents commercially available orunder clinical investigations are metal chelates containing paramagneticmetal ions, such as Fe³⁺, Gd³⁺, Mn²⁺, and Cu²⁺. When compared to othercontrast agents, the MRI contrast agents provide superior spatialresolution in tissues, and are safe due to the absence of exposure toX-rays or gamma radiation. The metal chelates have proved to beexceptionally well-tolerated class of contrast media. In particular,gadolinium MRI contrast agents do not show any nephrotoxicity incontrast to iodinated contrast media for CT (Runge, V. M. J. Magn.Reson. Imaging 2000, 12, 205-213).

Agents, which localize in bone and which provide MRI contrastenhancement, could be used to perform similar diagnostic proceduresemploying radiopharmaceuticals which localize in bone. Given thesubstantially greater spatial and temporal resolution of MRI techniques,as compared to nuclear medicine procedures, it is anticipated thatuseful diagnostic information could be obtained in abnormalities whichwere be able to be detected using radiopharmaceutical agents. The majordifference between radiopharmaceuticals and MRI contrast agents is thatradiopharmaceuticals are administered in very small dose and there islittle need to minimize the toxicity of these agents while MRI contrastagents are administered in relatively large quantities and it is oftendesirable to reduce the toxicity by maximizing water solubility.

Art in the MRI field is quite extensive, such that the followingsummary, not intended to be exhaustive, is provided only as references.Discussions of metal chelates of polyaminophosphonates as MRI contrastagents are found in U.S. Pat. No. 5,593,659, U.S. Pat. No. 5,342,606,U.S. Pat. No. 5,236,695, PCT patent application WO 97/31005, PCT patentapplication Wo 95/05118, PCT patent application Wo 94/26754, PCT patentapplication WO 92/08725, European patent application No.0468634, andEuropean patent application No.0210043. Functional tripodal chelants andthe use of their metal chelates in MRI imaging, x-ray imaging, andscintigraphic imaging are disclosed in PCT patent application No. WO95/01124, U.S. Pat. No. 5,565,184 and U.S. Pat. No. 5,450,601.

There is a continuing need for new and structurally diverse chelants andtheir metal chelants for use as MRI contrast agents or therapeuticradiopharmaceuticals for bone marrow suppression, bone pain relief, thetreatment of bone cancer, and various bone disorders. There is also afurther need to develop highly stable metal chelates with goodrelaxicity and osmolar characteristics.

Polydentate chelants with three-dimensional cavities are of greatinterest because of the high stability of the metal chelates, thesubstantial selectivity for certain metal ions, either by enforcing aspecific spatial arrangement of donor atoms or by introducing differentdonor atoms into the ligand backbone, and their capability to adopt apreorganized conformation in the unchelated form. The higher the degreeof preorganization of an unchelated ligand, the more stable the complexis.

Preorganization minimizes the freedom of motion of the donor atoms andthe chelant framework during the complexation process in such a way thatthe free ligand has a conformation more similar to that in the complex.Because of the restricted freedom of motion, the loss of entropy informing the complex is much less, which leads to the increasedthermodynamic stability of the metal chelate. Although preorganizationis a concept usually applied to macrocyclic and cryptate metalcomplexes, it is also of some importance for open-chain chelants. Forexample, metal complexes of CDTA (trans-cyclohexane-diaminetetraaceticacid) are often 2-3 orders of magnitude more stable than those of EDTA(ethylenediamine-tetraacetic acid) because of the restricted motion ofthe iminodiacetic chelating arms in CDTA.

Preorganization of a polydentate chelator results in not only highthermodynamic stability but also increased kinetic inertness of itsmetal chelate. This has been exemplified by the fact that the half-lifefor Gd(DOTA)⁻ in 0.1 M HCl is 60.2 h and 2000 years at pH=6.0 while thecomplex Gd(DTPA)²⁻ having comparable thermodynamic stability decomposesrapidly under acidic conditions (K_(obs)=1.2×10⁻³ s⁻¹; t_(1/2)˜1 min).The highly preorganized macrocyclic framework of DOTA forces fouraminoacetate chelating arms to adopt a conformation that the metal ioncan be wrapped in an N₄O₄ donor set. At the same, it is more difficultfor the coordinated acetate to be dissociated from the metal center.

There are several ways to achieve a high degree of preorganization for apolydentate chelant. These include the use of a macrocyclic ligandframework, the use of hydrogen bond(s) to enforce a three dimensionalcavity for metal coordination, and the choice of chelating arms. Polyaminocarboxylate ligands based on cyclen are known to be wellpreorganized and form highly stable lanthanide complexes due to theendocyclic orientation of the nitrogen donors. The siderophoreenterobactin forms much more stable Fe³⁺ complex than MECAM does becauseof the cyclic triester framework and hydrogen bonding (Garrett, T. M.,et al. J. Am. Chem. Soc. 1991, 113, 2965-2977; Stack, T. D. P., et al.J. Am. Chem. Soc. 1992, 114, 1512-1514; Tor, Y., et al. J. Am. Chem.Soc. 1992, 114, 6661-6671; Karpishin, T. B., et al J. Am. Chem. Soc.1993, 115, 182-192; Karpishin, T. B., et al. J. Am. Chem. Soc. 1993,115, 6115-6125; Meyer, M., et al. J. Am. Chem. Soc. 1997, 119,10093-10103.). Tripodal peptides with chiral conformations were found tobe stabilized by interstrand hydrogen bonds (Yakirevitch, P., et al.Inorg. Chem. 1993, 32, 1779-1787; Dayan, I., et al. Inorg. Chem. 1993,32, 1467-1475; Tor, Y., et al. J. Am. Chem. Soc. 1992, 114,6653-6661.).It was also found that hydrogen bonding plays a significant role in theconformation of the uncoordinated tripodal aminephenol ligands (Caravan,P., et al. J. Am. Chem. Soc. 1995, 117, 11230-11238; Yang, L-W., et al.Inorg. Chem. 1995, 34, 4921-4925; Liu, S., et al. Inorg. Chem. 1993, 32,4268; Liu, S., et al. Inorg. Chem. 1993, 32, 2773; Liu, S., et al.Inorg. Chem. 1993, 32, 1756; Liu, S., et al. Inorg. Chem. 1992, 31,5400; Liu, S., et al. J. Am. Chem. Soc. 1992, 114, 6081.) The use of acarbon atom as the bridgehead instead of a tertiary nitrogen atom alsolimits the motion of the aminephenol chelating arms. Renaud, et al(Chem. Commum. 1999, 457-458) reported C₃ symmetrical lanthanide podatesorganized by intramolecular trifurcated hydrogen bonds.

What really makes the new chelants described in this invention unique isthat the tripodal polyaminophosphonate chelant contains three chelatingarms, each of which contains three donor atoms (for example: amine-N,phenolate-O or pyridine-N, and phosphonate-O). As a result, they areexpected to form stable metal chelates with lanthanide metal ions, suchas Y³⁺, Sm³⁺, Gd³⁺, Dy³⁺, Ho³⁺, Yb³⁺, and Lu³⁺. Various spacers orbridging atoms are used to alter the degree of preorganization, therebythe thermodynamic stability and kinetic inertness of their metalchelates.

SUMMARY OF THE INVENTION

This invention relates to a novel class of tripodalpolyaminophosphonates and metal chelates thereof, methods of preparingthe tripodal polyaminophosphonate chelants and metal complexes, andpharmaceutical compositions comprising the tripodal polyaminophosphonatechelants and metal chelates. This invention relates particularly to theuse of the new metal chelates as contrast agents for x-ray or MRIimaging. This invention also relates to the use of metal chelates usefulas diagnostic radiopharmaceuticals for imaging the skeleton, myocardialinfarction, infarctions of the spleen and bowel, inflammatory boweldisease, radiation injury, metastastic calcification, bone cancer, andvarious bone disorders. This invention also relates to the use ofradiometal chelates particularly useful as therapeuticradiopharmaceuticals for bone pain relief, bone marrow suppression, thetreatment of bone cancer, and various bone disorders.

According to one embodiment of the present invention a tripodalpolyaminophosphonate chelant is provided, having the formula:

and pharmaceutically acceptable salts thereof, wherein

-   A is selected from: CR³, SiR³, GeR³, N, P, P═O, P═S, As, As═O and a    macrocyclic group having the formula:    —[C(L)R¹²(CR¹³R¹⁴)_(a)]_(b)—,    —[N(L)C(W)(CR¹⁵R¹⁶)_(c)]_(d)—,    —[OC(W)C(L)R¹⁷(CR¹⁸R¹⁹)_(e)]_(f) — or    {[NR²⁰C(W)C(L)R²¹(CR²²R²³)_(g)]_(h)[NR²⁴C(W)(CR²⁵R¹⁶)_(i)]_(j)}—,    -   wherein a is an integer selected from 1 to 3;    -   b is an integer selected from 3 to 5;    -   c is an integer selected from 1 to 3;    -   d is an integer selected from 3 or 4;    -   e is an integer selected from 1 to 3;    -   f is an integer selected from 3 or 4;    -   g is an integer selected from 1 to 3;    -   h is an integer selected from 3 or 4;    -   i is an integer selected from 1 to 3;    -   j is an integer selected from 0 to 3;    -   L is a direct bond to X;    -   W is H₂ or O;    -   R¹ is (CR⁴R⁵)_(n)R⁶, wherein    -   n is an integer selected from: 0 to 3;    -   R², R³, R⁴, R⁵, and R⁶ are independently selected from: H,        C₁-C₁₀ alkyl substituted with 0-5 R⁷, C₁-C₁₀ fluoroalkyl        substituted with 0-5 R⁷, C₂-C₁₀ alkenyl substituted with 0-5 R⁷,        C₂-C₁₀ fluoroalkenyl substituted with 0-5 R⁷, aryl substituted        with 0-5 R⁷ and fluroaryl substituted with 0-5 R⁷; or R⁴ and R⁵        may be taken together to form a C₃-C₁₀ cycloalkyl or C₃-C₁₀        cycloalkenyl optionally interrupted with C(O)NH, NH, NHC(O),        NHC(O)NH, NHC(S)NH, O, S, S(O), S(O)₂, P(O)(OR⁸), P(O)(OR⁸)O or        P(O)(NHR⁷)O, or aryl or fluoroaryl substituted with 0-5 R⁷;    -   R⁷ is selected from: H, OH, C(═O)R⁸, C(═O)OR⁸, C(═O)NR⁸ ₂,        PO(OR⁸)₂ and S(O)₂OR⁸;    -   R⁸ is selected from: H, C₁-C₆ alkyl, C₃-C₆ cycloalkyl, C₁-C₆        fluoroalkyl, C₁-C₆ alkenyl, C₃-C₆ cycloalkyl, C₁-C₆        fluoroalkenyl, benzyl, fluorobenzyl, phenyl and fluorophenyl;    -   X is selected from: (CR⁹R¹⁰)_(m), NR¹¹ or O(CR⁹R¹⁰)_(m), wherein        m is an integer selected from 1 to 3, provided that when A is N        or —[N(L)C(W)(CR¹⁵R¹⁶)_(c)]_(d)—, X is (CR⁹R¹⁰)_(m);    -   R⁹, R¹⁰ and R¹¹ are independently selected from: H or C₁-C₁₀        alkyl substituted with 0-5 R⁷, C₁-C₁₀ fluoroalkyl substituted        with 0-5 R⁷, C₂-C₁₀ alkenyl substituted with 0-5 R⁷, C₂-C₁₀        fluoroalkenyl substituted with 0-5 R⁷, aryl substituted with 0-5        R⁷, fluoroaryl substituted with 0-5 R⁷; or R⁹ and R¹⁰ may be        taken together to form a C₃-C₁₀ cycloalkyl or C₃-C₁₀        cycloalkenyl optionally interrupted with C(O)NH, NH, NHC(O),        NHC(O)NH, NHC(S)NH, O, S, S(O), S(O)₂, P(O)(OR⁸), P(O)(OR⁷)O,        P(O)(NHR⁷)O or aryl or fluoroaryl substituted with 0-5 R⁸; and    -   R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷, R¹⁸, R¹⁹, R²⁰, R²¹, R²², R²³, R²⁴,        R²⁵, and R²⁶ are independently selected at each occurrence from        H, C₁-C₆ alkyl, C₃-C₆ cycloalkyl, C₁-C₆ fluoroalkyl, C₁-C₆        alkenyl, C₃-C₆ cycloalkenyl, C₁-C₆ fluoroalkenyl, benzyl,        fluorobenzyl, phenyl and fluorophenyl.

According to another embodiment of the present invention, aradiopharmaceutical compound is provided, in which the tripodalpolyaminophosphonate chelant of the present invention is chelated with aradionuclide selected from: ⁶⁰Cu, ⁶²Cu, ⁶⁴Cu, ⁶⁷Cu, 68Ga, ^(99m)Tc,¹¹¹In, ⁹⁰Y, ¹⁴⁹Pr, ¹⁵³Sm, ¹⁵⁹Gd, ¹⁶⁶Ho, 169Yb, ¹⁷⁷Lu, ¹⁸⁶Re and ¹⁸⁸Re.

According to another embodiment of the present invention, an MRIcontrast agent is provided, in which the tripodal polyaminophosphonatechelant of the present invention is chelated with a paramagnetic metalion of atomic number 21-29, 42-44 or 58-70.

According to another embodiment of the present invention, an X-ray or CTcontrast agent is provided, in which the tripodal polyaminophosphonatechelant of the present invention is chelated with a heavy metal ion ofatomic number 21-31, 39-49, 50, 56-80, 82, 83 or 90.

According to another embodiment of the present invention, pharmaceuticalcompositions are provided for treating bone disorders that benefit fromthe delivery of cytotoxic doses of radiation in a patient in needthereof, containing the radiopharmaceutical compounds of the presentinvention and a pharmaceutically acceptable carrier. In yet anotherembodiment of the present invention treatment methods are provided fortreating bone disorders that benefit from the delivery of cytotoxicdoses of radiation in a patient in need thereof, in which an effectiveamount of the aforesaid pharmaceutical composition is administered tothe patient. In particular, the pharmaceutical compositions of thepresent invention may be used to relieve bone pain, suppress bone marrowand treat bone cancer, both primary and metastastic.

According to another embodiment of the present invention, radioactiveimaging compositions are provided containing the radiopharmaceuticalcompounds of the present invention and a pharmaceutically acceptablecarrier. In yet another embodiment of the present invention, methods forradioactive imaging are provided in which an effective amount of theradioactive imaging compositions of the present invention areadministered to a patient to be imaged sufficiently in advance thereto.The radioactive imaging compositions are, among other things, useful fordiagnosis of bone metastases, bone disorders, myocardial infarction,infarctions of the spleen and bowel, inflammatory bowel disease,radiation injury and metastastic calcification.

According to another embodiment of the present invention, magneticresonance imaging compositions are provided containing the magneticresonance imaging compounds of the present invention and apharmaceutically acceptable carrier. In yet another embodiment of thepresent invention, methods for magnetic resonance imaging are providedin which an effective amount of the magnetic resonance imagingcompositions of the present invention are administered to a patient tobe imaged sufficiently in advance thereto. The magnetic resonanceimaging compositions are, among other things, useful for diagnosis ofbone metastases, bone disorders, myocardial infarction, infarctions ofthe spleen and bowel, inflammatory bowel disease, radiation injury andmetastastic calcification.

According to another embodiment of the present invention, X-ray and CTimaging compositions are provided containing the X-ray and CT imagingcompounds of the present invention and a pharmaceutically acceptablecarrier. In yet another embodiment of the present invention, methods forX-ray and CT imaging are provided in which an effective amount of theX-ray or CT imaging compositions of the present invention areadministered to a patient to be imaged sufficiently in advance thereto.The X-ray and CT imaging compositions are, among other things, usefulfor diagnosis of bone metastases, bone disorders, myocardial infarction,infarctions of the spleen and bowel, inflammatory bowel disease,radiation injury and metastastic calcification.

According to another embodiment of the present invention, compositionsfor treating heavy metal toxicity in a patient in need thereof areprovided containing the polypodal chelant of the present invention and apharmaceutically acceptable carrier. In yet another embodiment of thepresent invention, methods for treating heavy metal toxicity in apatient in need thereof are provided in which an effective amount of theaforesaid compositions of the present invention are administered to thepatient.

Another embodiment of the present invention is diagnostic kits for thepreparation of radiopharmaceuticals or radioactive, magnetic resonance,X-ray or CT imaging agents. Diagnostic kits of the present inventioncomprise one or more vials containing the sterile, non-pyrogenic,formulation comprised of a predetermined amount of a compound of thepresent invention, and optionally other components such as one or twoancillary ligands, reducing agents, transfer ligands, buffers,lyophilization aids, stabilization aids, solubilization aids andbacteriostats. The inclusion of one or more optional components in theformulation will frequently improve the ease of synthesis of theradiopharmaceutical by the practicing end user, the ease ofmanufacturing the kit, the shelf-life of the kit, or the stability andshelf-life of the radiopharmaceutical. The one or more vials thatcontain all or part of the formulation can independently be in the formof a sterile solution or a lyophilized solid.

DETAILED DESCRIPTION OF THE INVENTION

Tripodal polyaminophosphonate chelants according to the presentinvention have the formula:

wherein A, X, R¹ and R² have the above-defined values. The spacer, A, ispreferably CR³, N and P═O, with R³ having the above-defined values. Morepreferably, A is CR³ or N, and most preferably N.

R¹ is preferably (CH₂)_(n)R⁶, with n preferably being 0 or 1. R², R³ andR⁶ are preferably independently selected from H, C₁-C₁₀ alkylsubstituted with 0-2 R⁷, C₁-C₁₀ fluoroalkyl substituted with 0-2 R⁷,C₂-C₁₀ alkenyl substituted with 0-2 R⁷, C₂-C₁₀ fluoroalkenyl substitutedwith 0-2 R⁷, aryl substi-tuted with 0-2 R⁷, fluroaryl substituted with0-2 R⁷ and heteroaryl substituted with 0-2 R⁷. More preferably, R² andR³ are independently selected from H, C₁-C₁₀ alkyl, C₁-C₁₀ fluoroalkyl,C₂-C₁₀ alkenyl, C₂-C₁₀ fluoroalkenyl, aryl and fluroaryl; and R⁶ is anaryl or heteroaryl group substituted with 0-2 R⁷. Even more preferably,R² is H and R³ is selected from H, C₁-C₁₀ alkyl and C₁-C₁₀ aryl.

R⁷ is preferably selected from H, OH, C(═O)OH, C(═O)NH₂, PO(OH)₂ andS(O)₂OH. More preferably, R⁷ is selected from H, OH, C(═O)OH, PO(OH)₂and S(O)₂OH.

X is preferably selected from (CH₂)_(m), NR¹¹ and O(CR⁹R¹⁰)_(m), whereinm is an integer selected from 1 to 3, wherein when A is N, X is(CH₂)_(m). More preferably, X is (CH₂)_(m), wherein m is 1 or 2.

-   -   R¹¹ is preferably selected from H, C₁-C₁₀ alkyl substituted with        0-2 R⁷, C₁-C₁₀ fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀        alkenyl substituted with 0-2 R⁷, C₂-C₁₀ fluoroalkenyl        substituted with 0-2 R⁷, aryl substituted with 0-2 R⁷ and        fluroaryl substituted with 0-2 R⁷.

Thus, preferred tripodal polyaminophosphonate chelants according to thepresent invention have the formula:

-   -   wherein R¹ is selected from phenyl, benzyl, imidazolyl, pyridyl        and thiophenyl, each substituted with 0-2 OH. A particularly        preferred tripodal polyaminophosphonate chelant has the formula:

Among preferred tripodal polyaminophosphonate chelants are chelants inwhich the phosphorous atoms include ³²P.

Definitions

The compounds herein described may have asymmetric centers. Compounds ofthe present invention containing an asymmetrically substituted atom maybe isolated in optically active or racemic forms. It is well known inthe art how to prepare optically active forms, such as by resolution ofracemic forms or by synthesis from optically active starting materials.Many geometric isomers of olefins, C═N double bonds, and the like canalso be present in the compounds described herein, and all such stableisomers are contemplated in the present invention. Cis and transgeometric isomers of the compounds of the present invention aredescribed and may be isolated as a mixture of isomers or as separatedisomeric forms. All chiral, diastereomeric, racemic forms and allgeometric isomeric forms of a structure are intended, unless thespecific stereochemistry or isomeric form is specifically indicated. Allprocesses used to prepare compounds of the present invention andintermediates made therein are considered to be part of the presentinvention.

The term “substituted,” as used herein, means that any one or morehydrogens on the designated atom is replaced with a selection from theindicated group, provided that the designated atom's normal valency isnot exceeded, and that the substitution results in a stable compound.When a substituent is keto (i.e., ═O), then 2 hydrogens on the atom arereplaced. Keto substituents are not present on aromatic moieties. When aring system (e.g., carbocyclic or heterocyclic) is said to besubstituted with a carbonyl group or a double bond, it is intended thatthe carbonyl group or double bond be part (i.e., within) of the ring.

The present invention is intended to include all isotopes of atomsoccurring in the present compounds. Isotopes include those atoms havingthe same atomic number but different mass numbers. By way of generalexample and without limitation, isotopes of hydrogen include tritium anddeuterium. Isotopes of carbon include C-13 and C-14.

When any variable (e.g., R⁹) occurs more than one time in anyconstituent or formula for a compound, its definition at each occurrenceis independent of its definition at every other occurrence. Thus, forexample, if a group is shown to be substituted with 0-2 R⁹, then saidgroup may optionally be substituted with up to two R⁹ groups and R⁹ ateach occurrence is selected independently from the definition of R⁹.Also, combinations of substituents and/or variables are permissible onlyif such combinations result in stable compounds.

When a bond to a substituent is shown to cross a bond connecting twoatoms in a ring, then such substituent may be bonded to any atom on thering. When a substituent is listed without indicating the atom via whichsuch substituent is bonded to the rest of the compound of a givenformula, then such substituent may be bonded via any atom in suchsubstituent. Combinations of substituents and/or variables arepermissible only if such combinations result in stable compounds.

As used herein, “alkyl” is intended to include both branched andstraight-chain saturated aliphatic hydrocarbon groups having thespecified number of carbon atoms. Examples of alkyl include, but are notlimited to, methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl,t-butyl, n-pentyl, and s-pentyl. “Haloalkyl” is intended to include bothbranched and straight-chain saturated aliphatic hydrocarbon groupshaving the specified number of carbon atoms, substituted with 1 or morehalogen (for example —C_(v)F_(w) where v=1 to 3 and w=1 to (2v+1)).Examples of haloalkyl include, but are not limited to, trifluoromethyl,trichloromethyl, pentafluoroethyl, and pentachloroethyl. “Alkoxy”represents an alkyl group as defined above with the indicated number ofcarbon atoms attached through an oxygen bridge. Examples of alkoxyinclude, but are not limited to, methoxy, ethoxy, n-propoxy, i-propoxy,n-butoxy, s-butoxy, t-butoxy, n-pentoxy, and s-pentoxy. “Cycloalkyl” isintended to include saturated ring groups, such as cyclopropyl,cyclobutyl, or cyclopentyl. Alkenyl” is intended to include hydrocarbonchains of either a straight or branched configuration and one or moreunsaturated carbon-carbon bonds which may occur in any stable pointalong the chain, such as ethenyl and propenyl. “Alkynyl” is intended toinclude hydrocarbon chains of either a straight or branchedconfiguration and one or more triple carbon-carbon bonds which may occurin any stable point along the chain, such as ethynyl and propynyl.

“Halo” or “halogen” as used herein refers to fluoro, chloro, bromo, andiodo; and “counterion” is used to represent a small, negatively chargedspecies such as chloride, bromide, hydroxide, acetate, and sulfate.

As used herein, “carbocycle” or “carbocyclic residue” is intended tomean any stable 3- to 7-membered monocyclic or bicyclic or 7- to13-membered bicyclic or tricyclic, any of which may be saturated,partially unsaturated, or aromatic. Examples of such carbocyclesinclude, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cycloheptyl, adamantyl, cyclooctyl, [3.3.0]bicyclooctane,[4.3.0]bicyclononane, [4.4.0]bicyclodecane, [2.2.2]bicyclooctane,fluorenyl, phenyl, naphthyl, indanyl, adamantyl, and tetrahydronaphthyl.

As used herein, the term “heterocycle” or “heterocyclic system” isintended to mean a stable 5- to 7-membered monocyclic or bicyclic or 7-to 10-membered bicyclic heterocyclic ring which is saturated partiallyunsaturated or unsaturated (aromatic), and which consists of carbonatoms and from 1 to 4 heteroatoms independently selected from the groupconsisting of N, O and S and including any bicyclic group in which anyof the above-defined heterocyclic rings is fused to a benzene ring. Thenitrogen and sulfur heteroatoms may optionally be oxidized. Theheterocyclic ring may be attached to its pendant group at any heteroatomor carbon atom which results in a stable structure. The heterocyclicrings described herein may be substituted on carbon or on a nitrogenatom if the resulting compound is stable. A nitrogen in the heterocyclemay optionally be quaternized. It is preferred that when the totalnumber of S and O atoms in the heterocycle exceeds 1, then theseheteroatoms are not adjacent to one another. It is preferred that thetotal number of S and O atoms in the heterocycle is not more than 1. Asused herein, the term “aromatic heterocyclic system” or “heteroaryl” isintended to mean a stable 5- to 7-membered monocyclic or bicyclic or 7-to 10-membered bicyclic heterocyclic aromatic ring which consists ofcarbon atoms and from 1 to 4 heterotams independently selected from thegroup consisting of N, O and S. It is preferred that the total number ofS and O atoms in the aromatic heterocycle is not more than 1.

Examples of heterocycles include, but are not limited to, acridinyl,azocinyl, benzimidazolyl, benzofuranyl, benzothiofuranyl,benzothiophenyl, benzoxazolyl, benzthiazolyl, benztriazolyl,benztetrazolyl, benzisoxazolyl, benzisothiazolyl, benzimidazolinyl,carbazolyl, 4aH-carbazolyl, carbolinyl, chromanyl, chromenyl,cinnolinyl, decahydroquinolinyl, 2H,6H-1,5,2-dithiazinyl,dihydrofuro[2,3-b]tetrahydrofuran, furanyl, furazanyl, imidazolidinyl,imidazolinyl, imidazolyl, 1H-indazolyl, indolenyl, indolinyl,indolizinyl, indolyl, 3H-indolyl, isobenzofuranyl, isochromanyl,isoindazolyl, isoindolinyl, isoindolyl, isoquinolinyl, isothiazolyl,isoxazolyl, methylenedioxyphenyl, morpholinyl, naphthyridinyl,octahydroisoquinolinyl, oxadiazolyl, 1,2,3-oxadiazolyl,1,2,4-oxadiazolyl, 1,2,5-oxadiazolyl, 1,3,4-oxadiazolyl, oxazolidinyl,oxazolyl, oxazolidinyl, pyrimidinyl, phenanthridinyl, phenanthrolinyl,phenazinyl, phenothiazinyl, phenoxathiinyl, phenoxazinyl, phthalazinyl,piperazinyl, piperidinyl, pteridinyl, purinyl, pyranyl, pyrazinyl,pyrazolidinyl, pyrazolinyl, pyrazolyl, pyridazinyl, pyridooxazole,pyridoimidazole, pyridothiazole, pyridinyl, pyridyl, pyrimidinyl,pyrrolidinyl, pyrrolinyl, 2H-pyrrolyl, pyrrolyl, quinazolinyl,quinolinyl, 4H-quinolizinyl, quinoxalinyl, quinuclidinyl,tetrahydrofuranyl, tetrahydroisoquinolinyl, tetrahydroquinolinyl,6H-1,2,5-thiadiazinyl, 1,2,3-thiadiazolyl, 1,2,4-thiadiazolyl,1,2,5-thiadiazolyl, 1,3,4-thiadiazolyl, thianthrenyl, thiazolyl,thienyl, thienothiazolyl, thienooxazolyl, thienoimidazolyl, thiophenyl,triazinyl, 1,2,3-triazolyl, 1,2,4-triazolyl, 1,2,5-triazolyl,1,3,4-triazolyl, and xanthenyl. Preferred heterocycles include, but arenot limited to, pyridinyl, furanyl, thienyl, pyrrolyl, pyrazolyl,pyrrolidinyl, imidazolyl, indolyl, benzimidazolyl, 1H-indazolyl,oxazolidinyl, benzotriazolyl, benzisoxazolyl, oxindolyl, benzoxazolinyl,and isatinoyl. Also included are fused ring and spiro compoundscontaining, for example, the above heterocycles.

A “diagnostic kit” or “kit” comprises a collection of components, termedthe formulation, in one or more vials which are used by the practicingend user in a clinical or pharmacy setting to synthesize diagnosticradiopharmaceuticals. The kit provides all the requisite components tosynthesize and use the diagnostic radiopharmaceutical except those thatare commonly available to the practicing end user, such as water orsaline for injection, a solution of the radionuclide, equipment forheating the kit during the synthesis of the radiopharmaceutical, ifrequired, equipment necessary for administering the radiopharmaceuticalto the patient such as syringes and shielding, and imaging equipment.

Buffers useful in the preparation of metallopharmaceut-icals and indiagnostic kits for the preparation of said radiopharmaceuticals includebut are not limited to phos-phate, citrate, sulfosalicylate, andacetate. A more com-plete list can be found in the United StatesPharmacopeia.

A “transfer ligand” is a ligand that forms an intermediate complex witha metal ion that is stable enough to prevent unwanted side-reactions butlabile enough to be converted to a metallopharmaceutical. The formationof the intermediate complex is kinetically favored while the formationof the metallopharmaceutical is thermodynamically favored. Transferligands useful in the preparation of metallopharmaceuticals and indiagnostic kits useful for the preparation of diagnosticradiopharmaceuticals include but are not limited to gluconate,glucoheptonate, mannitol, glucarate,N,N,N′,N′-ethylenediaminetetraacetic acid, pyro-phosphate andmethylenediphosphonate. In general, transfer ligands are comprised ofoxygen or nitrogen donor atoms.

A “reducing agent” is a compound that reacts with a radionuclide, whichis typically obtained as a relatively unreactive, high oxidation statecompound, to lower its oxidation state by transferring electron(s) tothe radionuclide, thereby making it more reactive. Reducing agentsuseful in the preparation of radiopharmaceuticals and in diagnostic kitsuseful for the preparation of said radiopharmaceuticals include but arenot limited to stannous chloride, stannous fluoride, formamidinesulfinic acid, ascorbic acid, cysteine, phosphines, and cuprous orferrous salts. Other reducing agents are described in Brodack et. al.,PCT Application 94/22496, which is incorporated herein by reference.

The phrase “pharmaceutically acceptable” is employed herein to refer tothose compounds, materials, compositions, and/or dosage forms which are,within the scope of sound medical judgment, suitable for use in contactwith the tis-sues of human beings and animals without excessivetoxicity, irritation, allergic response, or other problem orcompli-cation, commensurate with a reasonable benefit/risk ratio.

As used herein, “pharmaceutically acceptable salts” refer to derivativesof the disclosed compounds wherein the parent compound is modified bymaking acid or base salts thereof. Examples of pharmaceuticallyacceptable salts include, but are not limited to, mineral or organicacid salts of basic residues such as amines; and alkali or organic saltsof acidic residues such as carboxylic acids. The pharmaceuticallyacceptable salts include the conventional non-toxic salts or thequaternary ammonium salts of the parent compound formed, for example,from non-toxic inorganic or organic acids. For example, suchconventional non-toxic salts include those derived from inorganic acidssuch as hydrochloric, hydrobromic, sulfuric, sulfamic, phosphoric, andnitric; and the salts prepared from organic acids such as acetic,propionic, succinic, glycolic, stearic, lactic, malic, tartaric, citric,ascorbic, pamoic, maleic, hydroxymaleic, phenylacetic, glutamic,benzoic, salicylic, sulfanilic, 2-acetoxybenzoic, fumaric,toluenesulfonic, methanesulfonic, ethane disulfonic, oxalic, andisethionic.

The pharmaceutically acceptable salts of the present invention can besynthesized from the parent compound which contains a basic or acidicmoiety by conventional chemical methods. Generally, such salts can beprepared by reacting the free acid or base forms of these compounds witha stoichiometric amount of the appropriate base or acid in water or inan organic solvent, or in a mixture of the two; generally, nonaqueousmedia like ether, ethyl acetate, ethanol, isopropanol, or acetonitrileare preferred. Lists of suitable salts are found in Remington'sPharmaceutical Sciences, 17th ed., Mack Publishing Company, Easton, Pa.,1985, p. 1418, the disclosure of which is hereby incorporated byreference.

Since prodrugs are known to enhance numerous desirable qualities ofpharmaceuticals (e.g., solubility, bioavailability, manufacturing, etc .. . ) the compounds of the present invention may be delivered in prodrugform. Thus, the present invention is intended to cover prodrugs of thepresently claimed compounds, methods of delivering the same andcompositions containing the same. “Prodrugs” are intended to include anycovalently bonded carriers which release an active parent drug of thepresent invention in vivo when such prodrug is administered to amammalian subject. Prodrugs the present invention are prepared bymodifying functional groups present in the compound in such a way thatthe modifications are cleaved, either in routine manipulation or invivo, to the parent compound. Prodrugs include compounds of the presentinvention wherein a hydroxy, amino, or sulfhydryl group is bonded to anygroup that, when the prodrug of the present invention is administered toa mammalian subject, it cleaves to form a free hydroxyl, free amino, orfree sulfhydryl group, respectively. Examples of prodrugs include, butare not limited to, acetate, formate and benzoate derivatives of alcoholand amine functional groups in the compounds of the present invention.

“Stable compound” and “stable structure” are meant to indicate acompound that is sufficiently robust to survive isolation to a usefuldegree of purity from a reaction mixture, and formulation into anefficacious therapeutic agent.

The coordination sphere of the radionuclide includes all the ligands orgroups bound to the radionuclide. For a metallic radionuclide to bestable it typically has a coordination number (number of donor atoms)comprised of an integer greater than or equal to 4 and less than orequal to 9; that is there are 4 to 9 atoms bound to the metal and it issaid to have a complete coordination sphere. The requisite coordinationnumber for a stable radionuclide complex is determined by the identityof the radionuclide, its oxidation state, and the type of donor atoms.If the chelant does not provide all of the atoms necessary to stabilizethe metal radionuclide by completing its coordination sphere, thecoordination sphere is completed by donor atoms from other ligands,termed ancillary or co-ligands, which can also be either terminal orchelating.

Lyophilization aids useful in the preparation of diagnostic kits usefulfor the preparation of radiopharmaceuticals include but are not limitedto mannitol, lactose, sorbitol, dextran, Ficoll, andpolyvinylpyrrolidine (PVP).

Stabilization aids useful in the preparation of radiopharmaceuticals andin diagnostic kits useful for the preparation of saidradiopharmaceuticals include but are not limited to ascorbic acid,cysteine, monothioglycerol, sodium bisulfite, sodium metabisulfite,gentisic acid, and inositol.

Solubilization aids useful in the preparation of radio-pharmaceuticalsand in diagnostic kits for the preparation of radiopharmaceuticalsinclude but are not limited to etha-nol, glycerin, polyethylene glycol,propylene glycol, poly-oxyethylene sorbitan monooleate, sorbitanmonooleate, poly-sorbates,poly(oxyethylene)poly(oxypropylene)poly(oxyethyl-ene) block copolymers(Pluronics) and lecithin. Preferred solubilizing aids are polyethyleneglycol, and Pluronics.

Bacteriostats useful in the preparation of radiopharmaceuticals and indiagnostic kits useful for the preparation of said radiopharmaceuticalsinclude but are not limited to benzyl alcohol, benzalkonium chloride,chlorbutanol, and methyl, propyl or butyl paraben.

The technetium and rhenium radiopharmaceuticals of the present inventioncan be easily prepared by admixing a salt of a radionuclide, a compoundof the present invention, and a reducing agent, in an aqueous solutionat temperatures from 0 to 100° C. The technetium and rheniumradionuclides are preferably in the chemical form of pertechnetate orperrhenate and a pharmaceutically acceptable cation. The pertechnetatesalt form is preferably sodium pertechnetate such as obtained fromcommercial Tc-99m generators. The amount of pertechnetate used toprepare the radiopharmaceuticals of the present invention can range from0.1 mCi to 1 Ci, or more preferably from 1 to 200 mCi.

The amount of the compounds of the present invention used to prepare thetechnetium and rhenium radiopharma-ceuticals of the present inventioncan range from 0.01 μg to 10 mg, or more preferably from 0.5 μg to 200μg. The amount used will be dictated by the amounts of the otherreactants and the identity of the radiopharmaceuticals of the presentinvention to be prepared.

The metallopharmaceuticals of the present invention comprised of a metalof atomic number 21-31, 39-43, 44-50, 56-74, 76-80, 82-83, and 90 can beeasily prepared by admixing a salt of a radionuclide and a reagent ofthe present invention, in an aqueous solution at temperatures from 0 to100° C. These metals (radioisotopes, paramagnetic metals, and X-rayabsorbing metals) are typically obtained as a dilute aqueous solution ina mineral acid, such as hydrochloric, nitric or sulfuric acid. Themetals are combined with from one to about one thousand equivalents ofthe reagents of the present invention dissolved in aqueous solution. Abuffer is typically used to maintain the pH of the reaction mixturebetween 3 and 10.

The total time of preparation will vary depending on the identity of themetal ion, the identities and amounts of the reactants and the procedureused for the preparation. The preparations may be complete, resultingin >80% yield of the metallopharmaceutical, in 1 minute or may requiremore time. If higher purity metallopharmaceuticals are needed ordesired, the products can be purified by any of a number of techniqueswell known to those skilled in the art such as liquid chromatography,solid phase extraction, solvent extraction, dialysis or ultrafiltration.

Synthesis of Tripodal Polyaminophosponate Chelants

The present invention provides a new class of tripodalpolyaminophosphonate chelants that can rapidly form highly stable metalchelates useful as diagnostic or therapeuticmetalloradiopharmaceuticals, or magnetic resonance imaging contrastagents, or X-ray or CT contrast agents. In general, the tripodalpolyaminophosphonate chelants are composed of two parts: a spacerproviding the 3-D chelant framework and chelating arms for metalchelation. The spacer A can be built on a single bridging moietyselected from: R¹—C, R¹—Si, R¹—Ge, N, P, P(═O), or a cyclic group suchas 1,3,5-substituted cyclohexane. The spacer A is used in such a waythat all three chelating arms are properly arranged in the rightconformation for metal chelation. The chelating groups are not justlimited to carboxylates and may contain groups such as phosphonate,phosphinate, hydroxymate, hydroxylethyl, and hydroxyaryl.

The tripodal triamine A(X—NH₂)₃ is an important intermediate. Examplesof A(X—NH₂)₃ are shown in Chart I. Most of these tripodal amines areeither commercially available or can be readily prepared according tothe literature methods. For example, tris(2-aminoethyl)amine andtris(3-aminopropyl)amine are available from Aldrich.1,1,1-Tris(aminomethyl)ethane (TAME) and 1,2,3-triamino-propane can beprepared according to the procedure by Liu, et al (Inorg. Chem. 1993,32, 4268-4276 and Inorg. Chem. 1993, 32, 1756-1783);1,3,5-triaminocyclohexane by Bowen, T. et al (Bioorg. & Med. Chem. Lett.1996, 6, 807-810);tris-endo-tricyclo-[5.2.1.0^(4,10)]decane-2,5,8-triamine by Aguilera, A.et al (Synthetic Commun. 1991, 21, 1643-1648);2,2-bis(aminomethyl)-1,3-propanediamine by McAuley, A. et al (Can. J.Chem. 1989, 67, 1650-1656); 1,3,5-triamino-1,3,5-trideoxy-cis-inositolby Ghislett, M. et al (Helv. Chim. Acta 1992, 75, 2233-2251); germaniumtetrahydrazide by Singh, P. R. et al (Nucl. Med. Biol. 1994, 21,1115-1118); and trihydrazidophosphine oxide by Corlij, M. et al (J.Nucl. Biol. Med. 1992, 36, 296-300).

Once the tripodal triamine intermediate is available, synthesis of thetripodal polyaminophosphonate chelant is straightforward. In general,the triamine is allowed to react with three equivalents of aldehyde orketone to form the corresponding Schiff base (Chart II). The Schiff basecontains the imine C═N bonds, which can be reduced with a variety ofreducing agents to produce the corresponding amine (CH—NH) bonds.Diethylphosphite is as known reducing agent. In this invention,diethylphosphite was used for reductive addition of C═N bonds usingtetramethylguanidine as a catalyst according to the literature method(Tetrahedron letters 1998, 39, 7615-7618). The resulting product isdiethyl aminophosphinate, which can be readily hydrolyzed to give thecorresponding aminophosphonic acid.

The secondary amine group (Chart II) in the tripodalpolyaminophosphonate chelant can be further functionalized by alkylationof the amine-N atoms to give the corresponding functionalized tripodalpolyaminophosphonate chelant.

EXAMPLES

Instruments. ¹H NMR spectra were recorded on a 270 MHz Brukerspectrometer. The ¹H and ¹³C NMR data were reported as □ (ppm) relativeto TMS. Electrospray MS analyses were performed using a VG Quattro massspectrometer. LC-MS spectra were collected using a HP1100 LC/MSD systemwith API-electrospray interface. The high-performance liquid HPLCmethods used a Hewlett Packard Model 1090 instrument with radiometricdetector using a sodium iodide probe. The ITLC method used GelmanSciences ITLC paper strip, and a mixture of acetone and saline(50:50=v:v) as the mobile phase. Using this method, the metal chelatemigrate to the solvent front while the “metal colloid” and free metalion remain at the origin.

Diethylphosphite, tetramethylguanidine (TMG), andtris(2-aminoethyl)amine (tren) were purchased from Aldrich Chemical Co.,and were used without further purification.Tris((2-(salicylalideneamino)ethyl)amine)(H₃saltren) was preparedaccording to the literature method (Liu, S., et al. J. Am. Chem. Soc.1992, 114, 6081-6087).

Example I Synthesis ofTris(2-Aminoethyl)Amine-N,N′,N″-Tris(2-Hydroxybenzyl)MethylenephosphonicAcid (Tren(HBP)₃)

To a bright yellow solution of H₃saltren (0.92 g, 2.0 mmol) indiethylphosphite (15.0 mL) was added tetramethyl-guanidine (TMG, 0.3mL). The bright yellow color slowly disappeared (˜2 hr) upon stirring atroom temperature, indication that the Schiff based was completelyreduced. Excess diethylphosphite was removed to give a gummy liquid. Theresidue was dissolved in 6 N HCl (25 mL) and the mixture was heated toreflux overnight (15 hr). The resulting solution was cooled to roomtemperature, and the pH was adjusted to about 2 to give a pink solid.The solid was isolated by filtration, washed with water, and methanol,and dried under vacuum.

The crude product was dissolved in minimum amount of 5 NaOH solution togive a brownish color. The pH was then adjusted to ˜2 using theconcentrated HCl. The mixture was heated to reflux and the pink solidwas filtered, washed with methanol and dried under vacuum overnight. Thefiltrate was cooled to room temperature to give a white precipitate. Thesolid was collected by filtration, washed with methanol and dried undervacuum overnight. ES-MS (negative mode): m/e=726.8 for [M+Na−H]⁺(M=C₂₇H₃₉N₄O₁₂P₃); 363.2 for [M−2H]²⁻. ¹H NMR (in D₂+KOD): 7.25 (m, 3H,aromatic); 6.93 (t, 3H, aromatic); 6.46 (m, 6H, aromatic); 4.08 (dd, 3H,Ph-CH); and 2.2-2.4 (m, 12H, CH₂CH₂). ³¹P NMR (in D₂O+KOD): 18.6 ppm(relative to phosphoric acid).

Example II Synthesis of In-111 Complex of Tren(HBP)₃

To a clean 5 mL vial containing 0.5 mL of the Tren(HBP)₃ solution (4mg/mL in 0.5 M NH₄OAc, pH=7.5) was added 10 □L of ¹¹¹InCl₃ solution (˜1mCi) in 0.05 N HCl. The reaction mixture was heated at 80° C. for 15min. After cooling to room temperature, a sample of the resultingsolution was analyzed by ITLC. The yield was 98%.

Example III Synthesis of Y-90 Complex of Tren(HBP)₃

To a clean 5 mL vial containing 0.5 mL of the Tren(HBP)₃ solution (4mg/mL in 0.5 M NH₄OAc, pH=7.5) was added 15 □L of ⁹⁰YCl₃ solution (˜10mCi) in 0.05 N HCl. The reaction mixture was heated at 80° C. for 15min. After cooling to room temperature, the resulting solution wasanalyzed by ITLC. The yield was 97%.

Exmaple IV Synthesis of Lu-177 Complex of Tren(HBP)₃

To a clean 5 mL vial containing 0.5 mL of the Tren(HBP)₃ solution (4mg/mL in 0.5 M NH₄OAc, pH=7.5) was added 10 □L of ¹⁷⁷LuCl₃ solution (˜5mCi) in 0.05 N HCl. The reaction mixture was heated at 80° C. for 15min. After cooling to room temperature, the resulting solution wasanalyzed by ITLC. The yield was 95%.

Utility

The diagnostic radiopharmaceuticals are administered by intravenousinjection, usually in saline solution, at a dose of 1 to 100 mCi per 70kg body weight, or preferably at a dose of 5 to 50 mCi. Imaging isperformed using known procedures.

The therapeutic radiopharmaceuticals are administered by intravenousinjection, usually in saline solution, at a dose of 0.1 to 100 mCi per70 kg body weight, or preferably at a dose of 0.5 to 5 mCi per 70 kgbody weight.

The magnetic resonance imaging contrast agents of the present inventionmay be used in a similar manner as other MRI agents as described in U.S.Pat. No. 5,155,215; U.S. Pat. No. 5,087,440; Margerstadt et al., Magn.Reson. Med., 1986, 3, 808; Runge et al., Radiology, 1988, 166, 835; andBousquet et al., Radiology 1988, 166, 693. Generally, sterile aqueoussolutions of the contrast agents are administered to a patientintravenously in dosages ranging from 0.01 to 1.0 mmoles per kg bodyweight.

For use as X-ray contrast agents, the compositions of the presentinvention should generally have a heavy atom concentration of 1 mM to 5M, preferably 0.1 M to 2 M. Dosages, administered by intravenousinjection, will typically range from 0.5 mmol/kg to 1.5 mmol/kg,preferably 0.8 mmol/kg to 1.2 mmol/kg. Imaging is performed using knowntechniques, preferably X-ray computed tomography.

Other features of the invention will become apparent in the course ofthe following descriptions of exemplary embodiments which are given forillustration of the invention and are not intended to be limitingthereof.

This invention relates particularly to the use of the new metal chelatesas contrast agents for x-ray and MRI imaging. This invention alsorelates to the use of radiolanthanide metal chelates particularly usefulas therapeutic radiopharmaceuticals for bone pain relief, bone marrowsuppression, the treatment of bone cancer, and various bone disorders.

The radiopharmaceuticals of the present invention comprised of a gammaemitting isotope are useful for diagnosis of bone metastases, bonedisorders, myocardial infarction, infarctions of the spleen and bowel,inflam-matory bowel disease, radiation injury, as well as meta-stasticcalcification.

The radiopharmaceuticals of the present invention comprised of a beta,alpha or Auger electron emitting isotope are useful for bone painrelief, bone marrow suppression, the treatment of bone cancer, andvarious bone disorders, by delivering a cytotoxic dose of radiation tothe locus of the disease tissues.

The compounds of the present invention comprised of one or moreparamagnetic metal ions selected from gadolinium, dysprosium, iron, andmanganese, are useful as contrast agents for magnetic resonance imaging(MRI) of bone metastases, bone disorders, myocardial infarction,infarctions of the spleen and bowel, inflammatory bowel disease,radiation injury, as well as metastastic calcification.

The compounds of the present invention comprised of one or more heavyatoms with atomic number of 20 or greater are useful as X-ray contrastagents for X-ray imaging bone metastases, bone disorders, myocardialinfarction, infarctions of the spleen and bowel, inflammatory boweldisease, radiation injury, as well as metastastic calcification.

Biodistribution Study in Rats

Biodistribution of the radiopharmaceuticals was performed according tothe literature methods (Goeckeler et al. J. Nucl. Med. 1987, 28,495-504). Briefly, twenty to one hundred microliters of theradiopharmaceutical solution were injected to the tail veins ofunanesthetized Sprague Dawley rats (160-200 g) and each rat was housedindividually in a cage for 2 h. At 2 h postinjection the animals werescarified. One mililiter samples of blood were taken by cardiac punctureand weighed. The whole animals were then weighed and dissected. Theexcised tissues were washed with saline, blotted, and weighed prior tocounting. Cage droppings and kill papers were collected and counted withthe bladder to quantify the urine activity. One femur was excised anddissected free of soft tissues before weighing and counting. All tissuesremaining after the dissection were counted and marked as carcass. Thedata is collected in terms of the percentage of the injectedradioactivity per gram (% ID/g) of each specified type and bone/tissueratio of injected radioactivity.

For gamma scintigraphic imaging, 50-100 □Ci of the radiopharmaceuticalwere injected to the tail veins of unanesthetized Sprague Dawley rats(160-200 g). Serial images were collected for 2 hours with a 256×256matrix, no zoom, 5 minute dynamic images. A known source is placed inthe image field (20-90 μCi) to evaluate region of interest (ROI) uptake.Images were also acquired 24 hours post injection to determine retentionof the compound in the tissues. The uptake is determined by taking thefraction of the total counts in an inscribed area for ROI/source andmultiplying the known μCi. The result is μCi for the ROI. The data iscollected in terms of the percentage of the injected radioactivity (%ID) of each specified organ or tissue.

This model can also be used to assess the effectiveness of theradiopharmaceuticals of the present invention comprised of a beta, alphaor Auger electron emitting isotope. The radiopharmaceuticals areadministered in appropriate amounts and the uptake in the tumors can bequantified either non-invasively by imaging for those isotopes with acoincident imageable gamma emission, or by excision of the tissues andcounting the amount of radioactivity present by standard techniques.

This model can also be used to assess the compounds of the presentinvention comprised of paramagnetic metals as MRI contrast agents. Afteradministration of the appropriate amount of the paramagnetic compounds,the whole animal can be placed in a commercially available magneticresonance imager to image the tumors. The effectiveness of the contrastagents can be readily seen by comparison to the images obtain fromanimals that are not administered a contrast agent.

This model can also be used to assess the compounds of the presentinvention comprised of heavy atoms as X-ray contrast agents. Afteradministration of the appropriate amount of the X-ray absorbingcompounds, the whole animal can be placed in a commercially availableX-ray imager to image the tumors. The effectiveness of the contrastagents can be readily seen by comparison to the images obtain fromanimals that are not administered a contrast agent.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise that as specifically describedherein.

1. A tripodal polyaminophosphonate chelant having the formula:

and pharmaceutically acceptable salts thereof, wherein A is selectedfrom the group consisting of CR³, SiR³, GeR³, N, P, P═O, P═S, As, As═O,and a macrocyclic group having the formula:—[C(L)R¹²(CR¹³R¹⁴)_(a)]_(b)—,—[N(L)C(W)(CR¹⁵R¹⁶)_(c)]_(d)—,—[OC(W)C(L)R¹⁷(CR¹⁸R¹⁹)_(e)]_(f)— or—{[NR²⁰C(W)C(L)R²¹(CR²²R²³)_(g)]_(h)[NR²⁴C(W)(CR²⁵R¹⁶)_(i)]_(j)}—,wherein a is an integer selected from 1 to 3; b is an integer selectedfrom 3 to 5; c is an integer selected from 1 to 3; d is an integerselected from 3 or 4; e is an integer selected from 1 to 3; f is aninteger selected from 3 or 4; g is an integer selected from 1 to 3; h isan integer selected from 3 or 4; i is an integer selected from 1 to 3; jis an integer selected from 0 to 3; L is a direct bond to X; W is H₂ orO; R¹ is (CR⁴R⁵)_(n)R⁶, wherein n is an integer selected from 0 to 3; R²is selected from the group consisting of C₁-C₁₀ fluoroalkyl substitutedwith 0-5 R⁷, C₂-C₁₀ alkenyl substituted with 0-5 R⁷, C₂-C₁₀fluoroalkenyl substituted with 0-5 R⁷, aryl substituted with 0-5 R⁷,heteroaryl substituted with 0-5 R⁷ and fluoroaryl substituted with 0-5R⁷; R³, R⁴, R⁵ and R⁶ are independently selected from the groupconsisting of H, C₁-C₁₀ alkyl substituted with 0-5 R⁷, C₁-C₁₀fluoroalkyl substituted with 0-5 R⁷, C₂-C₁₀ alkenyl substituted with 0-5R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-5 R⁷, aryl substituted with0-5 R⁷, heteroaryl substituted with 0-5 R⁷ and fluoroaryl substitutedwith 0-5 R⁷; or R⁴ and R⁵ may be taken together to form a C₃-C₁₀cycloalkyl or C₃-C₁₀ cycloalkenyl optionally interrupted with C(O)NH,NH, NHC(O), NHC(O)NH, NHC(S)NH, O, S, S(O), S(O)₂, P(O)(OR⁸),P(O)(OR⁸)O, P(O)(NHR⁷)O, or to form an aryl substituted with 0-5 R⁷, afluoroaryl substituted with 0-5 R⁷ or an N-containing heterocyclesubstituted with 0-5 R⁷; R⁷ is selected from the group consisting of H,OH, C(═O)R⁸, C(═O)OR⁸, C(═O)NR⁸ ₂, PO(OR⁸)₂ and S(O)₂OR⁸; R⁸ is selectedfrom the group consisting of H, C₁-C₆ alkyl, C₃-C₆ cycloalkyl, C₁-C₆fluoroalkyl, C₁-C₆ alkenyl, C₃-C₆ cycloalkyl, C₁-C₆ fluoroalkenyl,benzyl, fluorobenzyl, phenyl and fluorophenyl; X is selected from thegroup consisting of (CR⁹R¹⁰)_(m), NR¹¹, and O(CR⁹R¹⁰)_(m), wherein m isan integer selected from 1 to 3, provided that when A is N or—[N(L)C(W)(CR¹⁵R¹⁶)_(c)]_(d)—, X is (CR⁹R¹⁰)_(m); R⁹, R¹⁰ and R¹¹ areindependently selected from the group consisting of H, C₁-C₁₀ alkylsubstituted with 0-5 R⁷, C₁-C₁₀ fluoroalkyl substituted with 0-5 R⁷,C₂-C₁₀ alkenyl substituted with 0-5 R⁷, C₂-C₁₀ fluoroalkenyl substitutedwith 0-5 R⁷, aryl substituted with 0-5 R⁷ and fluoroaryl substitutedwith 0-5 R⁷; or R⁹ and R¹⁰ may be taken together to form a C₃-C₁₀cycloalkyl or C₃-C₁₀ cycloalkenyl optionally interrupted with C(O)NH,NH, NHC(O), NHC(O)NH, NHC(S)NH, O, S, S(O), S(O)₂, P(O)(OR⁸),P(O)(OR⁷)O, P(O)(NHR⁷)O, or to form an aryl substituted with 0-5 R⁸ orfluoroaryl substituted with 0-5 R⁸; and R¹², R¹³, R¹⁴, R¹⁵, R¹⁶, R¹⁷,R¹⁸, R¹⁹, R²⁰, R²¹, R²², R²³, R²⁴, R²⁵, and R²⁶ are independentlyselected at each occurrence from the group consisting of H, C₁-C₆ alkyl,C₃-C₆ cycloalkyl, C₁-C₆ fluoroalkyl, C₁-C₆ alkenyl, C₃-C₆ cycloalkenyl,C₁-C₆ fluoroalkenyl, benzyl, fluorobenzyl, phenyl and fluorophenyl.
 2. Atripodal polyaminophosphonate chelant according to claim 1, wherein: Ais selected from the group consisting of CR³, N and P═O; R¹ is(CH₂)_(n)R⁶; R³ and R⁶ are independently selected from the groupconsisting of H, C₁-C₁₀ alkyl substituted with 0-2 R⁷, C₁-C₁₀fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀ alkenyl substituted with 0-2R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-2 R⁷, aryl substituted with0-2 R⁷, fluroaryl substituted with 0-2 R⁷ and heteroaryl substitutedwith 0-2 R⁷; X is selected from the group consisting of (CH₂)_(m), NR¹¹and O(CR⁹R¹⁰)_(m), wherein m is an integer selected from 1 to 3,provided that when A is N, X is (CH₂)_(m); and R¹¹ is selected from thegroup consisting of H, C₁-C₁₀ alkyl substituted with 0-2 R⁷, C₁-C₁₀fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀ alkenyl substituted with 0-2R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-2 R⁷, aryl substituted with0-2 R⁷ and fluroaryl substituted with 0-2 R⁷.
 3. A tripodalpolyaminophosphonate chelant according to claim 2, wherein: A is CR³ orN; n is 0 or 1; R³ is selected from the group consisting of H, C₁-C₁₀alkyl, C₁-C₁₀ fluoroalkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ fluoroalkenyl, aryland fluoroaryl; R⁶ is an aryl or heteroaryl group substituted with 0-2R⁷; R⁷ is selected from the group consisting of H, OH, C(═O)OH,C(═O)NH₂, PO(OH)₂ and S(O)₂OH; and X is (CH₂)_(m), wherein m is 1 or 2.4. A tripodal polyaminophosphonate chelant according to claim 3,wherein: A is CR³ or N; R³ is selected from the group consisting of H,C₁-C₁₀ alkyl and C₁-C₁₀ aryl; R⁶ is an aryl or heteroaryl groupsubstituted with 0-2 R⁷; R⁷ is selected from the group consisting of H,OH, C(═O)OH, PO(OH)₂ and S(O)₂OH; and X is (CH₂)_(m), wherein m is 1 or2.
 5. (cancelled)
 6. (cancelled)
 7. The tripodal polyaminophosphonatechelant of claim 1, wherein the phosphorous atoms in said chelantcomprise ³²P.
 8. A radiopharmaceutical compound comprising a tripodalpolyaminophosphonate chelant according to claim 1, chelated with aradionuclide selected from the group consisting of ^(52m)Mn, ⁵²Fe, ⁵⁵Co,⁶⁴Cu, ⁶⁷Cu, ⁶⁷Ga, ⁶⁸Ga, ⁹⁰Y, ^(94m)Tc, ^(99m)Tc, ¹⁰⁵Rh, ¹⁰⁹Pd, ¹¹¹In,^(117m)Sn, ¹⁴⁹Pr, ¹⁵³Sm, ¹⁵⁹Gd, ¹⁶⁶Ho, ¹⁶⁹Yb, ¹⁷⁷Lu, ¹⁸⁶Re, 188Re,²⁰³Pb, ²¹¹Pb, and ²¹²Bi.
 9. A radiopharmaceutical compound according toclaim 8, wherein: A is selected from the group consisting of CR³, N andP═O; R¹ is (CH₂)_(n)R⁶; R³ and R⁶ are independently selected from thegroup consisting of H, C₁-C₁₀ alkyl substituted with 0-2 R⁷, C₁-C₁₀fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀ alkenyl substituted with 0-2R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-2 R⁷, aryl substituted with0-2 R⁷, fluoroaryl substituted with 0-2 R⁷ and heteroaryl substitutedwith 0-2 R⁷; X is selected from the group consisting of (CR⁹R¹⁰)_(m),NR¹¹, and O(CR⁹R¹⁰)_(m), wherein m is an integer selected from 1 to 3,provided that when A is N, X is (CR⁹R¹⁰)_(m); R¹¹ is selected from thegroup consisting of H, C₁-C₁₀ alkyl substituted with 0-2 R⁷, C₁-C₁₀fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀ alkenyl substituted with 0-2R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-2 R⁷, aryl substituted with0-2 R⁷ and fluoroaryl substituted with 0-2 R⁷.
 10. A radiopharmaceuticalcompound according to claim 9, wherein: A is CR³ or N; n is 0 or 1; R³is independently selected from the group consisting of H, C₁-C₁₀ alkyl,C₁-C₁₀ fluoroalkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ fluoroalkenyl, aryl andfluroaryl; R⁶ is an aryl or heteroaryl group substituted with 0-2 R⁷; R⁷is selected from the group consisting of H, OH, C(═O)OH, C(═O)NH₂,PO(OH)₂ and S(O)₂OH; and X is (CH₂)_(m), wherein m is 1 or
 2. 11. Aradiopharmaceutical compound according to claim 10, wherein: A is CR³ orN; R³ is selected from the group consisting of H, C₁-C₁₀ alkyl andC₁-C₁₀ aryl; R⁶ is an aryl or heteroaryl group substituted with 0-2 R⁷;R⁷ is selected from the group consisting of H, OH, C(═O)OH, PO(OH)₂ andS(O)₂OH; and X is (CH₂)_(m), wherein m is 1 or
 2. 12. Aradiopharmaceutical compound according to claim 11, having the formula:

wherein R¹ is selected from the group consisting of phenyl, benzyl,imidazolyl, pyridyl and thiophenyl, each substituted with 0-2 OH.
 13. Aradiopharmaceutical compound according to claim 12, having the formula:


14. An MRI contrast agent comprising a tripodal polyaminophosphonatechelant according to claim 1, chelated with a paramagnetic metal ion ofatomic number 21-29, 42-44 or 58-70.
 15. An MRI contrast agent accordingto claim 14, wherein: A is selected from the group consisting of CR³, Nand P═O; R¹ is (CH₂)_(n)R⁶, R² is selected from the group consisting ofC₁-C₁₀ fluoroalkyl substituted with 0-5 R⁷, C₂-C₁₀ alkenyl substitutedwith 0-5 R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-5 R⁷, arylsubstituted with 0-5 R⁷, heteroaryl substituted with 0-5 R⁷ andfluoroaryl substituted with 0-5 R⁷; R³ and R⁶ are independently selectedfrom the group consisting of H, C₁-C₁₀ alkyl substituted with 0-2 R⁷,C₂-C₁₀ fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀ alkenyl substitutedwith 0-2 R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-2 R⁷, arylsubstituted with 0-2 R⁷, fluoroaryl substituted with 0-2 R⁷ andheteroaryl substituted with 0-2 R⁷; X is selected from the groupconsisting of (CR⁹R¹⁰)_(m), NR¹¹, and O(CR⁹R¹⁰)_(m), wherein m is aninteger selected from 1 to 3, provided that when A is N, X is(CR⁹R¹⁰)_(m); R¹¹ is selected from the group consisting of H, C₁-C₁₀alkyl substituted with 0-2 R⁷, C₁-C₁₀ fluoroalkyl substituted with 0-2R⁷, C₂-C₁₀ alkenyl substituted with 0-2 R⁷, C₂-C₁₀ fluoroalkenylsubstituted with 0-2 R⁷, aryl substituted with 0-2 R⁷ and fluroarylsubstituted with 0-2 R⁷.
 16. An MRI contrast agent according to claim15, wherein: A is CR³ or N; n is 0 or 1; R³ is selected from the groupconsisting of H, C₁-C₁₀ alkyl, C₁-C₁₀ fluoroalkyl, C₂-C₁₀ alkenyl,C₂-C₁₀ fluoroalkenyl, aryl and fluroaryl; R⁶ is an aryl or heteroarylgroup substituted with 0-2 R⁷; R⁷ is selected from the group consistingof H, OH, C(═O)OH, C(═O)NH₂, PO(OH)₂ and S(O)₂OH; and X is (CH₂)_(m),wherein m is 1 or
 2. 17. An MRI contrast agent according to claim 16,wherein: A is CR³ or N; R³ is selected from the group consisting of H,C₁-C₁₀ alkyl and C₁-C₁₀ aryl; R⁶ is an aryl or heteroaryl groupsubstituted with 0-2 R⁷; R⁷ is selected from the group consisting of H,OH, C(═O)OH, PO(OH)₂ and S(O)₂OH; and X is selected from: (CH₂)_(m),wherein m is 1 or
 2. 18. An MRI contrast agent according to claim 17,wherein said tripodal polyaminophosphonate chelant has the formula:

wherein R¹ is selected from the group consisting of phenyl, benzyl,imidazolyl, pyridyl and thiophenyl, each substituted with 0-2 OH.
 19. AnMRI contrast agent according to claim 18, wherein said tripodalpolyaminophosphonate chelant has the formula:


20. An X-ray or CT contrast agent comprising a tripodalpolyaminophosphonate chelant according to claim 1, chelated with a heavymetal ion of atomic number 21-31, 39-50, 56-80, 82, 83 or
 90. 21. AnX-ray or CT contrast agent according to claim 20, wherein: A is selectedfrom the group consisting of CR³, N and P═O; R¹ is (CH₂)_(n)R⁶, R³ andR⁶ are independently selected from the group consisting of H, C₁-C₁₀alkyl substituted with 0-2 R⁷, C₁-C₁₀ fluoroalkyl substituted with 0-2R⁷, C₂-C₁₀ alkenyl substituted with 0-2 R⁷, C₂-C₁₀ fluoroalkenylsubstituted with 0-2 R⁷, aryl substituted with 0-2 R⁷, fluoroarylsubstituted with 0-2 R⁷ and heteroaryl substituted with 0-2 R⁷; X isselected from the group consisting of (CR⁹R¹⁰)_(m), NR¹¹, andO(CR⁹R¹⁰)_(m), wherein m is an integer selected from 1 to 3, providedthat when A is N, X is (CR⁹R¹⁰)_(m); R¹¹ is selected from the groupconsisting of H, C₁-C₁₀ alkyl substituted with 0-2 R⁷, C₁-C₁₀fluoroalkyl substituted with 0-2 R⁷, C₂-C₁₀ alkenyl substituted with 0-2R⁷, C₂-C₁₀ fluoroalkenyl substituted with 0-2 R⁷, aryl substituted with0-2 R⁷ and fluoroaryl substituted with 0-2 R⁷.
 22. An X-ray or CTcontrast agent according to claim 21, wherein: A is CR³ or N; n is 0 or1; R³ is selected from the group consisting of H, C₁-C₁₀ alkyl, C₁-C₁₀fluoroalkyl, C₂-C₁₀ alkenyl, C₂-C₁₀ fluoroalkenyl, aryl and fluroaryl;R⁶ is an aryl or heteroaryl group substituted with 0-2 R⁷; R⁷ isselected from the group consisting of H, OH, C(═O)OH, C(═O)NH₂, PO(OH)₂and S(O)₂OH; and X is (CH₂)_(m), wherein m is 1 or
 2. 23. An X-ray or CTcontrast agent according to claim 22, wherein: A is CR³ or N; R³ isselected from the group consisting of H, C₁-C₁₀ alkyl and C₁-C₁₀ aryl;R⁶ is an aryl or heteroaryl group substituted with 0-2 R⁷; R⁷ isselected from the group consisting of H, OH, C(═O)OH, PO(OH)₂ andS(O)₂OH; and X is selected from: (CH₂)_(m), wherein m is 1 or
 2. 24. AnX-ray or CT contrast agent according to claim 23, wherein said tripodalpolyaminophosphonate chelant has the formula:

wherein R¹ is selected from the group consisting of phenyl, benzyl,imidazolyl, pyridyl and thiophenyl, each substituted with 0-2 OH.
 25. AnX-ray or CT contrast agent according to claim 24, wherein said tripodalpolyaminophosphonate chelant has the formula:


26. A radiopharmaceutical composition for treating bone disorders thatbenefit from the delivery of cytotoxic doses of radiation to the bonetissues of a patient in need thereof, comprising a therapeuticallyeffective amount of the tripodal poly-aminophosphonate chelant of claim7 and a pharmaceutically acceptable carrier.
 27. A method for treatingbone disorders that benefit from the delivery of cytotoxic doses ofradiation to the bone tissues of a patient in need thereof, comprisingadministering to said patient an effective amount of theradiopharmaceutical composition of claim
 26. 28. The method of claim 27,wherein said method comprises relieving bone pain, suppressing bonemarrow or treating bone cancer.
 29. The method of claim 28, wherein saidmethod comprises treating bone cancer.
 30. The method of claim 29,wherein the bone cancer comprises a primary tumor.
 31. The method ofclaim 29, wherein the bone cancer tumor comprises a secondary tumor. 32.A composition for radioactive imaging comprising an effective amount ofthe radiopharmaceutical compound of claim 8 and a pharmaceuticallyacceptable carrier, wherein the radio-nuclide is selected from the groupconsisting of ^(52m)Mn, ⁵²Fe, ⁵⁵Co, ⁶⁴Cu, ⁶⁰Cu, ⁶²Cu, ⁶⁷Ga, ⁶⁸Ga,^(94m)Tc, ^(99m)Tc, and ¹¹¹In.
 33. A method for radioactive imagingcomprising administering to a patient to be imaged sufficiently inadvance thereto an effective amount of the radioactive imagingcomposition of claim
 32. 34. A method according to claim 33, whereinsaid method is for imaging bone metastases, bone disorders, myocardialinfarction, infarctions of the spleen and bowel, inflammatory boweldisease, radiation injury and metastastic calcification.
 35. A methodaccording to claim 33, wherein said imaging method is gamma scintigraphyor positron-emission tomography.
 36. A composition for X-ray imagingcomprising an effective amount of the contrast agent of claim 20 and apharmaceutically acceptable carrier.
 37. A method for X-ray imagingcomprising administering to a patient to be imaged sufficiently inadvance thereof an effective amount of the X-ray imaging composition ofclaim
 36. 38. A method according to claim 37, wherein said method is forimaging bone metastases, bone disorders, myocardial infarction,infarctions of the spleen and bowel, inflammatory bowel disease,radiation injury and metastastic calcification.
 39. A method accordingto claim 37, wherein said X-ray imaging method is CT imaging.
 40. Acomposition for magnetic resonance imaging comprising an effectiveamount of the contrast agent of claim 14 and a pharmaceuticallyacceptable carrier.
 41. A method for magnetic resonance imagingcomprising administering to a patient to be imaged sufficiently inadvance thereof an effective amount of the magnetic resonance imagingcomposition of claim
 40. 42. A method according to claim 41, whereinsaid method is for imaging bone metastases, bone disorders, myocardialinfarction, infarctions of the spleen and bowel, inflammatory boweldisease, radiation injury and metastastic calcification.
 43. Apharmaceutical composition for treating heavy metal toxicity in apatient in need thereof, comprising a therapeutically effective amountof the tripodal polyaminophosphonate chelant of claim 1 and apharmaceutically acceptable carrier.
 44. A method for treating heavymetal toxicity in a patient in need thereof, comprising administering tosaid patient a therapeutically effective amount of the pharmaceuticalcomposition of claim
 43. 45. A radiopharmaceutical treatment kitcomprising: a sterile, non-pyrogenic formulation comprising aradiopharmaceutical composition according to claim 26, a pH 3-9buffering agent and optionally one or more additives selected from thegroup consisting of ancillary ligands, reducing agents, transferligands, buffers, lyophilization aids, stabilization aids,solubilization aids, bacteriostats and equipment for administering saidcomposition.
 46. The treatment kit of claim 45, wherein said formulationis in the form of a sterile solution or lyophilized solid.
 47. Adiagnostic kit comprising: a sterile, non-pyrogenic formulationcomprising a radiopharmaceutical composition according to claim 32, a pH3-9 buffering agent and optionally one or more additives selected fromthe group consisting of ancillary ligands, reducing agents, transferligands, buffers, lyophilization aids, stabilization aids,solubilization aids, bacteriostats and equipment for administering saidcomposition.
 48. The diagnostic kit of claim 47, wherein saidformulation is in the form of a sterile solution or lyophilized solid.49. A diagnostic kit comprising: a sterile, non-pyrogenic formulationcomprising an X-ray imaging composition according to claim 36, a pH 3-9buffering agent and option-ally one or more additives selected from thegroup consisting of ancillary ligands, reducing agents, transferligands, buffers, lyophilization aids, stabilization aids,solubilization aids, bacteriostats and equipment for administering saidcomposition.
 50. The diagnostic kit of claim 49, wherein saidformulation is in the form of a sterile solution or lyophilized solid.51. A diagnostic kit comprising: a sterile, non-pyrogenic formulationcomprising a magnetic resonance imaging composition according to claim40, a pH 3-9 buffering agent and optionally one or more additivesselected from the group consisting of ancillary ligands, reducingagents, transfer ligands, buffers, lyophilization aids, stabilizationaids, solubilization aids, bacteriostats and equipment for administeringsaid composition.
 52. The diagnostic kit of claim 51, wherein saidformulation is in the form of a sterile solution or lyophilized solid.53. A radiopharmaceutical composition for treating bone disorders thatbenefit from the delivery of cytotoxic doses of radiation to the bonetissues of a patient in need thereof, comprising a therapeuticallyeffective amount of the radiopharmaceutical compound of claim 8 and apharmaceutically acceptable carrier.
 54. A method for treating bonedisorders that benefit from the delivery of cytotoxic doses of radiationto the bone tissues of a patient in need thereof, comprisingadministering to said patient an effective amount of theradiopharmaceutical composition of claim
 53. 55. The method of claim 54,wherein said method comprises relieving bone pain, suppressing bonemarrow or treating bone cancer.
 56. The method of claim 55, wherein saidmethod comprises treating bone cancer.
 57. The method of claim 56,wherein the bone cancer comprises a primary tumor.
 58. The method ofclaim 56, wherein the bone cancer tumor comprises a secondary tumor. 59.A radiopharmaceutical treatment kit comprising: a sterile, non-pyrogenicformulation comprising a radiopharmaceutical composition according toclaim 53, a pH 3-9 buffering agent and optionally one or more additivesselected from the group consisting of ancillary ligands, reducingagents, transfer ligands, buffers, lyophilization aids, stabiliza-tionaids, solubilization aids, bacteriostats and equipment for administeringsaid composition.
 60. The treatment kit of claim 59, wherein saidformulation is in the form of a sterile solution or lyophilized solid.